Hemodynamic characteristics at anterior communicating artery before aneurysm initiation using patient-specific finite element blood flow simulations

The anterior communicating artery (AComA) is a unique vascular location that receives blood from two sources of inflow and redistributes it toward the anterior part of the brain through two efferent arteries. It is widely accepted that complexity in the flow pattern is associated with the high rate of aneurysm formation in that location observed in large studies. A previous computational hemodynamic study showed a possible association between high maximum intraaneurysmal wall shear stress (WSS) at the systolic peak with rupture in a cohort of AComA aneurysms. In another study it was observed a connection between location of aneurysm blebs and regions of high WSS in models where blebs were virtually removed. The purpose of this work is to study associations between hemodynamic patterns and AComA aneurysm initiation by comparing hemodynamics between the aneurysm models and the normal model where the aneurysm was computationally removed. Vascular models of both right and left circulation were independently reconstructed from three-dimensional rotational angiography images using deformable models after image registration of both images, and later fused using a surface merging algorithm. Afterwards, the geometric models were used to generate high-quality volumetric finite element grids composed several million tetrahedral elements with an advancing front technique. For each patient the second anatomical model was created by digitally removing the aneurysm. It was iteratively achieved by applying a Laplacian smoothing filter and remeshing the surface. Finite element blood flow numerical simulations were performed for both the pathological and normal models under the same flow conditions. Personalized pulsatile flow conditions were imposed at the inlets of both models with use of the Womersley solution. The Navier-Stokes equations were numerically integrated by using a fully implicit finite-element formulation. From analysis of WSS distributions it was observed that aneurysms initiated in regions of high and moderate WSS in the counterpart normal models. Adjacent or close to those regions, low WSS portions of the arterial wall were not affected by the disease. These results are in line with previous reported observations at other vascular locations.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. George Mason University; Estados UnidosFil: Putman, Christopher M.. Inova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido

Hemodynamic characteristics at anterior communicating artery before aneurysm initiation using patient-specific finite element blood flow simulations

The anterior communicating artery (AComA) is a unique vascular location that receives blood from two sources of inflow and redistributes it toward the anterior part of the brain through two efferent arteries. It is widely accepted that complexity in the flow pattern is associated with the high rate of aneurysm formation in that location observed in large studies. A previous computational hemodynamic study showed a possible association between high maximum intraaneurysmal wall shear stress (WSS) at the systolic peak with rupture in a cohort of AComA aneurysms. In another study it was observed a connection between location of aneurysm blebs and regions of high WSS in models where blebs were virtually removed. The purpose of this work is to study associations between hemodynamic patterns and AComA aneurysm initiation by comparing hemodynamics between the aneurysm models and the normal model where the aneurysm was computationally removed. Vascular models of both right and left circulation were independently reconstructed from three-dimensional rotational angiography images using deformable models after image registration of both images, and later fused using a surface merging algorithm. Afterwards, the geometric models were used to generate high-quality volumetric finite element grids composed several million tetrahedral elements with an advancing front technique. For each patient the second anatomical model was created by digitally removing the aneurysm. It was iteratively achieved by applying a Laplacian smoothing filter and remeshing the surface. Finite element blood flow numerical simulations were performed for both the pathological and normal models under the same flow conditions. Personalized pulsatile flow conditions were imposed at the inlets of both models with use of the Womersley solution. The Navier-Stokes equations were numerically integrated by using a fully implicit finite-element formulation. From analysis of WSS distributions it was observed that aneurysms initiated in regions of high and moderate WSS in the counterpart normal models. Adjacent or close to those regions, low WSS portions of the arterial wall were not affected by the disease. These results are in line with previous reported observations at other vascular locations.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. George Mason University; Estados UnidosFil: Putman, Christopher M.. Inova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido

Effects of Casson rheology on aneurysm wall shear stress

It is widely accepted that wall shear stress plays an important role in cerebral aneurysm initiation, progress and rupture. Previous works have shown strong evidence in support of the high wall shear stress as a risk factor associated to those biomechanical processes. Patient-specific imagebased computational hemodynamic modeling of vascular systems harboring cerebral aneurysms has demonstrated to be a fast and reliable way to compute quantities difficult or impossible to be measured in-vivo. The accuracy of the simulation results have been successfully validated in the past. Additionally, most model assumptions have shown no impact on the flow characterization whose association with the mentioned processes was investigated. Particularly, the incorporation of the blood rheology in large arterial systems containing aneurysms resulted in similar hemodynamic characterizations for most aneurysms. However, large aneurysms, especially those containing blebs are expected to have flow rates in the range where Newtonian and non-Newtonian models exhibit the largest differences. In order to study the impact of blood rheology in vascular systems harboring specific intracranial aneurysms, unsteady finite element blood flow simulations were carried out over patient-specific models. Those models were reconstructed from rotational angiographic images using region growing and deformable model algorithms. Unstructured finite element meshes were generated using and advancing front technique. Walls were assumed as rigid, traction-free boundary conditions were imposed at the outlets of the models, and a flow rate wave form was imposed at the inlets after scaling according to the Murray's Law for optimal arterial networks. The Casson model was incorporated as a velocity gradient dependent apparent viscosity and the results were compared to those using the Newtonian rheology. Regions with differentiated wall shear stress values and orientations were studied.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Secretaria de Ciencia y Técnica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada, Maria Carolina. Universidad Favaloro. Facultad de Ingeniería y Ciencias Exactas y Naturales; ArgentinaFil: Putman, Christopher M.. Innova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido

Estimation of Aneurysm Wall Motion from 4D Computerized Tomographic Angiography Images

It is widely accepted that wall shear stressis associated to aneurysm formation, growthand rupture. Early identification of potential risk factors may contribute to decide the treatment and improve patient care. Previous studies have shown associations between high aneurysm wall shear stress values and both elevated risk of rupture and localization of regions of aneurysm progression. Based on the assumption that damaged regions of the endothelium have different mechanical properties, regions with differentiated wall displacement amplitudes are expected. A previous approach based on the analysis ofbidimensional dynamic tomographic angiography images at a limited number of points during the cardiac cycle showed only small displacements in some patients using that simplified and semi-automatic low resolution methodology. The purpose of this work is to overcome some of those limitations. High time and spatial resolution four dimensional computerized tomographic angiography images of cerebral aneurysms were acquired and analyzed in order to identify and characterize wall motion. Images were filtered andsegmented at nineteentime points during the cardiac cycle.An average image was computed to generate the vascular model. Anunstructured mesh of tetrahedral elements was generated using an advancing front technique. A finite element blood flow simulationwas carried out under personalized pulsatile flow conditions. A fuzzy c-means clustering algorithm was used to estimate regions that exhibit wall motion within the aneurysm sac. A good correlation between localization of regions of elevated wall shear stress and regionsexhibiting wall motion was found.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada Olivares, María C.. Universidad Favaloro; ArgentinaFil: Putman, Christopher M. . Inova Fairfax Hospital. Department of Interventional Neuroradiology; Estados UnidosFil: Cebral, Juan R.. George Mason University. Department of Computational and Data Sciences; Estados Unido

Effects of Casson rheology on aneurysm wall shear stress

It is widely accepted that wall shear stress plays an important role in cerebral aneurysm initiation, progress and rupture. Previous works have shown strong evidence in support of the high wall shear stress as a risk factor associated to those biomechanical processes. Patient-specific imagebased computational hemodynamic modeling of vascular systems harboring cerebral aneurysms has demonstrated to be a fast and reliable way to compute quantities difficult or impossible to be measured in-vivo. The accuracy of the simulation results have been successfully validated in the past. Additionally, most model assumptions have shown no impact on the flow characterization whose association with the mentioned processes was investigated. Particularly, the incorporation of the blood rheology in large arterial systems containing aneurysms resulted in similar hemodynamic characterizations for most aneurysms. However, large aneurysms, especially those containing blebs are expected to have flow rates in the range where Newtonian and non-Newtonian models exhibit the largest differences. In order to study the impact of blood rheology in vascular systems harboring specific intracranial aneurysms, unsteady finite element blood flow simulations were carried out over patient-specific models. Those models were reconstructed from rotational angiographic images using region growing and deformable model algorithms. Unstructured finite element meshes were generated using and advancing front technique. Walls were assumed as rigid, traction-free boundary conditions were imposed at the outlets of the models, and a flow rate wave form was imposed at the inlets after scaling according to the Murray's Law for optimal arterial networks. The Casson model was incorporated as a velocity gradient dependent apparent viscosity and the results were compared to those using the Newtonian rheology. Regions with differentiated wall shear stress values and orientations were studied.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional. Secretaria de Ciencia y Técnica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ahumada, Maria Carolina. Universidad Favaloro. Facultad de Ingeniería y Ciencias Exactas y Naturales; ArgentinaFil: Putman, Christopher M.. Innova Fairfax Hospital; Estados UnidosFil: Cebral, Juan Raúl. George Mason University; Estados Unido

Reconstructing Deconstruction: High-Velocity Cloud Distance Through Disruption Morphology

We present Arecibo L-band Feed Array 21-cm observations of a sub-complex of HVCs at the tip of the Anti-Center Complex. These observations show morphological details that point to interaction with the ambient halo medium and differential drag within the cloud sub-complex. We develop a new technique for measuring cloud distances, which relies upon these observed morphological and kinematic characteristics, and show that it is consistent with H-alpha distances. These results are consistent with distances to HVCs and halo densities derived from models in which HVCs are formed from cooling halo gas.Comment: 8 pages, 2 figures, 1 tabe, Accepted to Ap

Hemodynamic Analysis of Intracranial Aneurysms with Moving Parent Arteries: Basilar Tip Aneurysms

The effects of parent artery motion on the hemodynamics of basilar tip saccular aneurysms and its potential effect on aneurysm rupture were studied. The aneurysm and parent artery motions in two patients were determined from cine loops of dynamic angiographies. The oscillatory motion amplitude was quantified by registering the frames. Patient‐specific computational fluid dynamics (CFD) models of both aneurysms were constructed from 3D rotational angiography images. Two CFD calculations were performed for each patient, corresponding to static and moving models. The motion estimated from the dynamic images was used to move the surface grid points in the moving model. Visualizations from the simulations were compared for wall shear stress (WSS), velocity profiles, and streamlines. In both patients, a rigid oscillation of the aneurysm and basilar artery in the anterio‐posterior direction was observed and measured. The distribution of WSS was nearly identical between the models of each patient, as well as major intra‐aneurysmal flow structures, inflow jets, and regions of impingement. The motion observed in pulsating intracranial vasculature does not have a major impact on intra‐aneurysmal hemodynamic variables. Parent artery motion is unlikely to be a risk factor for increased risk of aneurysmal rupture

Leatherback Turtles in the Eastern Gulf of Mexico: Foraging and Migration Behavior During the Autumn and Winter

We deployed 19 satellite tags on foraging adult leatherback turtles, including 17 females and 2 males, captured in the northeastern Gulf of Mexico in 2015, 2018, and 2019 in order to study regional distribution and movements. Prior to our study, limited data were available from leatherbacks foraging in the Gulf of Mexico. Tag deployment durations ranged from 63 to 247 days and turtles exhibited three distinct behavior types: foraging, transiting, or rapidly switching between foraging and transiting. Some females were tracked to nesting beaches in the Caribbean. Most of the leatherbacks remained on and foraged along the west Florida continental shelf whereas a few individuals foraged in waters of the central Gulf of Mexico during the autumn and winter. In addition, migration of adult females through the Yucatan Channel indicate that this is a seasonally important area for Caribbean nesting assemblages

Simulation of intracranial aneurysm stenting: Techniques and challenges

Recently, there has been considerable interest in the use of stents as endovascular flow diverters for the treatment of intracranial aneurysms. Simulating this novel method of treatment is essential for understanding the intra-aneurysmal hemodynamics in order to design better stents and to personalize and optimize the endovascular stenting procedures. This paper describes a methodology based on unstructured embedded grids for patient-specific modeling of stented cerebral aneurysms, demonstrates how the methodology can be used to address specific clinical questions, and discusses remaining technical issues. In particular, simulations are presented on a number of patient-specific models constructed from medical images and using different stent designs and treatment alternatives. Preliminary sensitivity analyses with respect to stent positioning and truncation of the stent model are presented. The results show that these simulations provide useful and valuable information that can be used during the planning phase of endovascular stenting interventions for the treatment of intracranial aneurysms

Computational fluid dynamics of stented intracranial aneurysms using adaptive embedded unstructured grids

Recently, there has been increased interest in the use of stents as flow diverters in the endovascular treatment of cerebral aneurysms as an alternative to surgical clipping or endovascular embolization with coils. The aim of aneurysm stenting is to block the flow into the aneurysm in order to clot the blood inside the aneurysm and effectively isolate it from the circulation and prevent bleeding from the aneurysm. A hybrid meshing approach that combines body‐fitted grids for the vessels and adaptive embedded grids for the stents is proposed and analyzed. This strategy simplifies considerably the geometry modeling problem and allows accurate patient‐specific hemodynamic simulations with endovascular devices. This approach is compared with the traditional body‐fitted approach in the case of the flow around a circular cylinder at representative Reynolds number and an idealized aneurysm model with a stent. A novel technique to map different stent designs to a given patient‐specific anatomical model is presented. The methodology is demonstrated on a patient‐specific hemodynamic model of an aneurysm of the internal carotid artery constructed from a 3D rotational angiogram and stented with two different stent designs. The results show that the methodology can be successfully used to model patient‐specific anatomies with different stents thereby making it possible to explore different stent design